Osteoarthritis is a degenerative disease of the knee joint which results in chronic pain to the subject when the knee joint is loaded. The pain can be present even when the knee joint is statically loaded, such as when the subject is standing. The pain is particularly apparent, however, when the knee joint is dynamically loaded, such as when the subject is engaging in routine daily activities or exercising.
Although osteoarthritis is commonly held to be a disease of the middle aged or elderly, it also occurs in younger populations, e.g., between about 30 to 40 years of age, as the result of knee joint overuse, injury, or previous surgery. Whereas an elderly individual may have relatively modest dynamic requirements for the knee joint, a younger individual is typically more active and has more rigorous dynamic requirements for the knee joint. Accordingly, any treatment of osteoarthritis must address dynamic as well as static loading of the knee joint.
Osteoarthritic pain is caused by an unbalanced loading on the medial or lateral compartment of the knee joint which closes the clearance space forming the compartment between the condyles of the femur and tibia. When there is contact of the condyles in the respective compartment of the knee joint, and particularly dynamic contact, abrasion occurs at the contact surface producing pain in the joint. Relatively mild osteoarthritic pain can be treated with pain reducing drugs. Invasive surgery, however, has often been the treatment of choice for more advanced cases of osteoarthritis causing debilitating pain. Surgery, nevertheless, may not provide effective long-term correction of the condition because degeneration of the knee joint frequently continues even after initial surgical correction. Accordingly, follow-up surgical procedures can be required to restore and maintain the joint, thereby diminishing the desirability of surgery as a treatment alternative.
As such, a need exists for effective and noninvasive means of relieving pain associated with degenerative diseases of the knee joint, and particularly pain associated with osteoarthritis of the knee joint. U.S. Pat. No. 5,277,698 discloses a brace designed to reduce the effect of osteoarthritis by applying a corrective principle force directly to a single point on the knee joint. The single force point is located posterior to the axis of knee joint rotation on the side of the knee joint opposite the afflicted joint compartment. The principle force is applied by means of a compliant strap contacting the knee joint at the force point. The strap is anchored to the upper and lower leg cuffs of the brace and follows a helical pathway around the knee joint.
Although the brace of U.S. Pat. No. 5,277,698 may reduce the effect of osteoarthritis on the knee joint as the joint approaches full extension, the brace is believed to be ineffective in reducing the effect of osteoarthritis across the entire dynamic range of motion of the knee joint, particularly when the joint is in flexion. The brace of U.S. Pat. No. 5,277,698 is mounted on the leg of a user by presetting the length of the principle force-producing strap. The length is not readily adjustable thereafter as long as the knee joint remains dynamic. Accordingly, the degree of strap tension that can be applied to the knee joint across a range of flexion angles is significantly limited due to slackening of the fixed-length strap at greater flexion angles.
It is nevertheless believed that the greatest treatment benefit to the user is achieved during the swing phase of gait when the knee is flexed and bears no body weight. In this phase it is possible for the corrective force applied by the brace to the knee joint to approach the magnitude of the unbalanced load on the unweighted knee joint, thereby effectively offsetting the imbalance. By comparison, the load on the fully-extended knee joint during the weight-bearing phase of gait is substantially greater than the unweighted load on the knee joint. Osteoarthritic treatment is impractical during the weight-bearing phase because the load on the knee joint is too great to be effectively offset by known braces without applying treatment forces above those tolerable by the user. Thus, any osteoarthritic brace failing to maintain a predictably sustained and tolerable treatment force on the knee joint across the range of flexion angles encountered during the swing gait phase is not an effective treatment means.
UK Patent Application No. GB 2 136 294A discloses a knee brace for treatment of osteoarthritis that substitutes a sling for the helical strap of U.S. Pat. No. 5,277,698 as the principle means of applying the treatment force to the side of the knee joint. Unlike the helical strap, the sling distributes the treatment force across a surface of the joint rather than applying the principle treatment force to a single point posterior to the axis of rotation of the knee joint. The force applied by the sling to the knee joint is nevertheless a function of strap tension because the sling is secured to the brace cuffs by a plurality of straps. Accordingly, the brace of the UK Patent Application is likewise inadequate for dynamic stabilization of an osteoarthritic knee joint.
It is also noted that the braces of UK Patent Application No. GB 2 136 294A and U.S. Pat. No. 5,277,698 both have means for controlling flexion of the knee joint that are connected to the leg cuffs and are positioned on the side of the knee joint opposite the side to which the principle treatment force is applied when the brace is in place on the leg. The knee flexion controlling means are distinguishable from one another, however, insofar as U.S. Pat. No. 5,277,698 employs a rotatable hinge, while UK Patent Application No. GB 2 136 294A employs a piston in parallel with a flexible rod.
U.S. Pat. No. 4,632,098 discloses a knee brace that maintains a padded rigid plate, rather than the above-described sling or strap, in engagement with a side of the knee joint. The brace has a knee rotation controlling means similar to the flexible rod of UK Patent Application No. GB 2 136 294A, but the flexible rod of U.S. Pat. No. 4,632,098 is positioned on the same side of the brace as the knee engaging member, i.e., the plate, and the rod is rigidly connected to the plate and rigid cuffs of the brace. In addition to connection with the rod, the plate is also secured to the brace in an opposing direction by a plurality of flexible straps extending from the plate to the cuffs.
The specific configuration of connectors attaching the plate to the cuffs and rod renders the brace of U.S. Pat. No. 4,632,098 inapplicable to osteoarthritic knee joints. The forces on the plate from the rod and straps tend to cancel one another, preventing the plate from applying an effective treatment force to the side of the knee joint opposite the afflicted compartment of the joint, as required of an osteoarthritic knee brace.
Other knee braces are known in the prior art to provide resilient pads that contact the side of the knee joint as exemplified by U.S. Pat. Nos. 3,581,741 and 5,002,045. The pads, however, merely cushion the leg from the brace while facilitating retention of the brace in position on the leg. The pads primarily exert a tangential frictional force on the side of the knee joint, applying no significant radial treatment force to the side of the joint. The frictional force is incidental to the principle force applied by the cuffs to the upper and lower legs. Like the brace of U.S. Pat. No. 4,632,098, such braces have little relevance to the treatment of osteoarthritis in the knee joint.
It is, therefore, an object of the present invention to provide an orthopedic brace for treatment of degenerative disease in the knee joint, and more particularly for the treatment of osteoarthritis in the knee joint. It is further an object of the present invention to provide an osteoarthritic knee brace that effectively relieves the user of knee joint pain throughout a broad dynamic range of knee joint motion, and particularly in the swing phase of gait. It is another object of the present invention to provide an osteoarthritic knee brace that is readily adjustable to the specific requirements of the user. It is a further object of the present invention to provide an osteoarthritic knee brace that is comfortable for the user to wear and can be worn continuously, if desired, in routine daily activities as well as strenuous physical activities without unduly limiting the mobility of the user. These objects and others are achieved by the invention described hereafter.